Is there a link between abuse in childhood and pain disorders?

Keywords::

• abuse
• childhood
• maltreatment
• pain

Childhood maltreatment is a major public health problem, with nearly 1 million verified cases annually in the USA. Many more cases are unverified or unreported. According to US Child Protective Services data from the 2007 report of the Child Welfare Information Gateway, 60% of reported cases involve neglect, and approximately a quarter involve physical, sexual or psychological abuse. In the setting of this too often silent epidemic, there is growing evidence that childhood maltreatment has long-term consequences affecting health [1,2]. Epidemiological studies, including those of prospective design, demonstrate strong associations between childhood maltreatment and obesity [3,4], cigarette smoking [5], substance abuse [6] and depressed or anxious mood [7,8]. However, an area of growing interest and considerable controversy has been the relationship of childhood maltreatment and pain disorders [9,10], including headache, fibromyalgia, irritable bowel syndrome, pelvic pain and back pain. In this editorial, I will recap and comment on the epidemiological studies that have fueled the debate, and outline the growing scientific evidence that led me to affirm the link, and to be optimistic that further research on the neurobiological sequelae of abuse will eventually enhance pain prevention and treatment.

Results from a large number of survey studies in adults, some with thousands of participants, have suggested an association of childhood maltreatment with pain in adulthood. The lack of uniformity in the findings, particularly in the links between specific abuse and pain subtypes, is not unexpected given the wide range of geographic locations, populations and survey methodologies that these studies encompass. In addition, a vast array of clinical criteria has been used to define and quantify both abuse and pain. For example, emotional abuse, which is more elusive and insidious than physical and sexual abuse, has only recently been recognized as a distinct form of maltreatment. And although it has thus far received less scientific and public attention to date, studies suggest emotional abuse may have more lasting consequences and be particularly deleterious when combined with other abuse types [11]. Despite their diversity and complexity, survey studies have demonstrated overall a relationship between abuse and pain [9], with pain condition (and severity) depending, in part, on abuse intensity, duration, timing and perpetrator. The dose-dependent nature of the association is further suggested by the finding that more abuse types correlates with a greater likelihood of multiple pain disorders in adulthood [12].

As a growing number of survey studies strengthen the case for a true abuse–pain association, the retrospective nature of these studies is at the heart of the debate [10,13]. Asking questions years after an event, survey studies introduce the potential for recall bias. Time, plus the very nature of a physically or psychologically traumatic event, may interfere with accurate memory, and lead to under-reporting of abuse. However, other factors come into play that could introduce bias in the opposite direction. Populations seeking healthcare may be more prone to give positive responses to questions, including those regarding prior abuse. However, a number of nonclinical populations, including student and general populations, have shown similar results. There is also concern that depressed mood, which is strongly associated with abuse, may cause a person to perceive past experiences in a negative light, and thereby over-report abuse. Similarly, depression and anxiety may lower the pain threshold and amplify one’s perception of pain severity. I acknowledge these possibilities, whilst entertaining an alternative theory that the link between depression and pain, rather than being causal, is reflective of a shared etiology, in this case abuse-induced physiological changes. Regardless of the mechanism, a number of studies, including four from general populations [14–17], have established that although depression influences the strength of the association, an independent relationship exists between abuse and pain.

The debate is also fuelled by the findings from two intriguing prospective studies [16,18], interviewing adults regarding pain complaints years after court-documented evidence of abuse as children. Neither study demonstrated an association between abuse and pain. Interestingly, however, both reported a relationship between abuse and pain when abuse was defined by self-report rather than by court document. The contradictory nature of the findings from the retrospective versus prospective perspective begs explanation. Although a prospective method of case ascertainment eliminates the recall bias inherent in retrospective studies, accuracy may still be obscured by the fact that abuse is an under-reported event. In the larger of the two studies, the retrospective analysis suggests that some individuals in the ‘nonabused’ control group may have been misclassified, thus minimizing an association between abuse and pain [18]. It has also been suggested that detecting, reporting and treating abuse may alter the likelihood that it will have the same sequelae (i.e., pain) that occur in those in whom it is unreported and unaddressed [13]. That said, there is one prospective study that suggests an impact of abuse on pain beginning later in childhood [19]. Another prospective population-based study found that in adults who were pain-free at enrollment, self-reported childhood abuse was associated on 2-year follow-up with back pain and physical limitations [20]. This supports the accuracy of self-reporting methodology.

The question of whether childhood abuse actually leads to adult pain cannot be answered by epidemiological studies, but scientific evidence may offer clues to pathophysiology. Much of the research has focused on the effects of stress on the regulation of the hypothalamic–pituitary–adrenal axis, although inconsistencies in the findings have made the extent and manner by which childhood abuse has an impact uncertain. Findings from a recent long-term longitudinal study following nonstress morning cortisol levels in sexually abused females from childhood through to young adulthood suggest that abuse leads to a period of cortisol hypersecretion followed by hyposecretion [21]. Whether the attenuated response is deleterious or adaptive is uncertain, but lower cortisol levels have been reported in individuals with fibromyalgia, endometriosis and chronic pelvic pain. Other functional changes linked to early life stress include enhanced electrical irritability in limbic structures and reduced activity of the cerebellar vermis [22]. Early stressful experiences also appear to lead to a number of structural neurobiological consequences, including reduced corpus callosum size, and attenuated development of the left neocortex, hippocampus and amygdalae [22], all implicated as part of the so-called pain matrix. A recent diffusion tensor imaging study in young adults exposed to parental verbal abuse revealed cerebral white matter tract abnormalities that have been associated with limbic irritability, depression, anxiety and somatization [23]. Childhood maltreatment has been newly described to be associated with and predictive of inflammation in adulthood, through the measurement of biomarkers [24]. Finally, although there has long been suspicion that certain genotypes predict resilience of vulnerability to environmental stressors, such as adverse experiences, recent clinical [25] and preclinical work [26] has highlighted the possibility that childhood abuse and early life stress may become hard-coded into the genome, creating an epigenetic memory of events that lead to impaired health at a later date.

In answer to the question, “is there a link between abuse in childhood and pain disorders?”, I believe the answer is ‘yes’, but I think that there is much more to learn. This leads to the question that is perhaps raised even more often in response to this topic – that of whether patients seeking help for painful conditions should be routinely asked about childhood abuse. I have been asking about abuse for over a decade, but my answer is still a qualified ‘no’. Past abuse increases the likelihood of conditions, such as depression and anxiety, that could have an impact on health and well-being, but most clinicians screen for these important comorbidities directly. I recognize that many individuals abused as children are revictimized as adults, but again, the safety of the home environment is already part of our routine patient assessment. In the patients I see with headache, a large portion of my outpatient practice, I utilize cognitive–behavioral strategies, in addition to medications, regardless of the past history, so the knowledge of childhood abuse doesn’t yet alter my management strategy. I emphasize yet, because with the emerging scientific study evidence that early-life stress alters neurobiological systems, right down to the level of DNA, there is hope on the horizon that we may eventually understand the intricacies of the abuse–pain relationship, and devise better pain prevention and treatment strategies.

Financial & competing interests disclosure

The author has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.